Overlay network technologies, such as Virtual Extensible Local Area Networks (VXLANs), offer a highly scalable solution to managing cloud computing deployments by allowing OSI layer 2 networks to expand beyond layer 3 network boundaries through network virtualization. Layer 2 data traffic, such as Media Access Control (MAC) Ethernet frames, can be encapsulated within layer 3 packets, such as User Datagram Protocol (UDP) packets, to travel across layer 3 boundaries to reach its destination within the overlay network.
Various tunnel endpoints within the overlay network, such as Virtual Tunnel Endpoints (VTEPs), can terminate overlay network packets by encapsulating and de-encapsulating packets through MAC-to-UDP encapsulation. Each tunnel endpoint may be provided with a unique IP/MAC address pair to make the encapsulation and routing encapsulated packets within the overlay network possible. In an overlay network such as a VXLAN network or Network Virtualization using Generic Routing Encapsulation (NVGRE), the associations between host addresses and tunnel endpoints are typically created by a central controller and those mappings are distributed to all the tunnel endpoints in the overlay network.
In environments such as large-scale data centers, the database storing these mappings can grow very large and consume a large amount of storage resources at individual tunnel endpoints all across the network. Besides the storage requirements, any change in this database would then need to be distributed from the central controller and processed at every tunnel endpoint. Thus, the amount of storage and processing required to maintain a central routing table imposes a significant constraint to the number of hosts an overlay network can support. In addition, this requirement makes it more difficult to implement overlay processing in hardware to improve traffic throughput because of the silicon area limitation. Having one single central server may also mean that there exists a single point of failure, which tends to increase security risks.